Field of the Invention
The present invention relates to an ink, an ink cartridge, and an ink jet recording method.
Description of the Related Art
The recording speed of ink jet recording apparatuses has been dramatically improved as a result of the technical advance. Such ink jet recording apparatuses have been gradually introduced into the field of business document printing in place of laser recording apparatuses. Ink jet recording apparatuses typically use, as inks for texts to be used for recording images on recording media such as plain paper, aqueous inks containing self-dispersible pigments as a coloring material in consideration of high optical density.
The aqueous ink contains water as a liquid medium and thus has an advantage in terms of environment. However, water can dissolve a trace amount of oxygen, and thus an ink incorporates oxygen with time when being in contact with the air. When the oxygen incorporated into an ink oxidizes constituent materials of the ink, unnecessary functional groups may be formed, or decomposition reaction may proceed. This causes a problem of physical property variation of the ink. When the physical properties of an ink are changed, images to be recorded may be so affected as not to maintain the initially intended properties, for example.
To solve the problems caused by the oxidation of constituent materials, the addition of various additives to an ink has been studied. For example, a dye ink containing an antioxidant has been disclosed in order to improve the storage stability (Japanese Patent Application Laid-Open No. S63-139962). It has been also disclosed to add an antioxidant in order to reduce the oxidation of a dispersion resin used in a nonaqueous ink (Japanese Patent Application Laid-Open No. 2005-290035). In addition, a composition containing an antioxidant and an ultraviolet absorber in combination has been disclosed in order to improve the light resistance of images (Japanese Patent Application Laid-Open No. 2000-034433).
However, the results of studies by the inventors of the present invention have shown that the additives such as antioxidants that have been thought to be effective are not always effective for the aqueous ink including a self-dispersible pigment as a coloring material.
An object of the present invention is thus to provide an aqueous ink containing a self-dispersible pigment as a coloring material but having physical properties for which variation due to oxidation is reduced and enabling the recording of high quality images even after storage. The present invention is also directed to provide an ink cartridge including the aqueous ink and an ink jet recording method using the aqueous ink.